Hand held probe for measuring tire tread wear

ABSTRACT

A hand-held probe ( 10 ) for measuring a tire tread profile comprises a housing ( 20 ) with a slit ( 64 ) formed parallel to its major axis, a range finder ( 70 ) mounted inside the housing ( 20 ) in such a way that it can traverse much of the length of the tube while directing light from a laser through a window ( 60 ) and onto a tire surface, a bracket ( 50 ) that is carried by the proximal end of the tube to enable the user to hold the probe ( 10 ) in position against the tire, a serial port ( 32 ) for connection with a computer ( 40 ), and a handle ( 30 ) that houses the batteries for operation and an IR or RF transmitter. The IR or RF transmitter is for transmitting the tire tread profile wirelessly to a computer suitably equipped to receive IR or RF transmissions.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application No.60/115,915, filed on Jan. 14, 1999, which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to devices for measuring tire tread wear.More specifically, the present invention is a device for determining thetread profile by electro-optical measurements so that tread wear can bequantified.

BACKGROUND OF THE INVENTION

Tire treads are defined by a number of grooves or channels cut into theperipheral portion of the tire. The treads are the portions of theperiphery that come into contact with the road.

Tire treads give tires traction in cornering and stopping. Tire treads,however, wear during the course of use. Eventually, treads wear to thepoint where their ability to provide traction is compromised and thetire needs to be replaced or recapped.

Because tire treads wear slowly, and the amount of wear from day to dayor week to week is imperceptible, frequent checking is unnecessary. Yet,unless a tire is checked for the depth of its treads at some reasonableinternal, an excessively worn tire can be overlooked. Checking tiretread depth at intervals can allow a reasonably prediction as to whenthe tire will need to be replaced. Furthermore, such a prediction cannotbe made, and, indeed, the amount of tread remaining can be difficult toquantify, without a measurement.

Many states have requirements about the condition of the treads of atire and require the replacement of tires when they become excessivelyworn. Fleet managers may have their own internal requirements forreplacement of tires that are worn based on tread depth or after aspecified number of miles. Simple gauges or rulers are simply notaccurate enough. Accurate measurement of tire tread depth is difficultto do without removing the tire and measuring the tread with specialelectro-optical measuring devices. See for example, the patents of Subeet al issued Sep. 21, 1993, U.S. Pat. No. 5,245,867, and Dory et al,issued Oct. 5, 1993, U.S. Pat. No. 5,249,460. In order to obtain anaccurate measurement, the tire is suspended so that it is not engaging asurface. These devices are expensive and require a good deal of time andeffort for checking the depth of the tread of a single tire. However,there remains a need for accurate tire tread depth measurement that doesnot have the defects of the prior art and that measures the profile ofthe tire tread so that tread depth ran be quantified.

SUMMARY OF THE INVENTION

According to its major aspects and briefly recited, the presentinvention is a probe for measuring the profile of a tire tread. A tiretread profile is a two-dimensional plot of the distance from each pointon a fixed reference line running across the tire from side to side tothe nearest point on the tire surface. This plot will show thedifferences in the distances to the line for the treads and the channelsand thus the amount of wear on the treads. The hand held probe comprisesa housing with a slit formed parallel to its major axis, a handleattached to the proximal end of the housing, a range finder mountedinside the housing in such a way that it can traverse much of the lengthof the tube while directing light from a laser through a window mountedover the slit, and a bracket that is carried near the proximal end ofthe tube to enable the user to hold the probe in position against thetire. The output from the device is via a computer port proximate to thehandle or an IR or RP transmitter from the end of the handle. Power issupplied to the device by batteries in the handle.

The housing of the probe is placed against the tire with the slit andits window facing the tread. Preferably, the housing has an concavearcuate portion formed therein to define two edges of the housing thatcan act as supports on either side of the window to rest against thetire. When the device is pushed laterally toward the near side of thetire until it engages the tire, the device is then stabilized and inposition to make a measurement. With the housing thus in position, thereference line with respect to the tire is set. The device is activatedby pressing an “on” button, causing the range finder to determine thedistance from the range finder to the tire as the range finder slowlytraverses the length of the housing. The distance data—in terms of x andy coordinates—is fed to the computer via either the computer port on theproximal end of the housing or the IR or RF window on the end of thehandle. The computer can display the distance to the tread and tochannels between treads as output, thus displaying the profile of thetire. A compute suitably programmed with local tread requirements canalso determine if the tire is acceptable or not.

An advantage of the present device is its simplicity of use. The bracketand arcuate housing make it easy to position against the tire so that itis stable. The computer port that supports data transmission to acomputer make the results of the measurement quickly available to theuser via any computer.

Another advantage of the present invention is that it provides a tiretread profile rather than a series of single distance measurements. Theprofile of a tire provides more information than any single measurementand is a more reliable indicator of tread wear than a series ofindividual measurements, and quicker to obtain.

The IR or RP window in the base of the handle is still another featureof the present invention. This window makes it possible to avoid use ofa cable when operating the present handheld tire tread profiler.

Other features and their advantages will be apparent to those skilled inthe art of tread depth measurement from a carefull reading of theDetailed Description of Preferred Embodiments accompanied by thefollowing drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a perspective view of the probe according to a preferredembodiment of the preset invention played against a tire;

FIG. 2 is a side, cross sectional view of a detail of the housing of theprobe of FIG. 1; and

FIG. 3 is a view of a display on the computer on the probe of FIG. 1with a sample display.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is a hand-held probe for measuring the depth oftire treads. Tire treads are integral, radial projections about thecircumference of a vehicular tire separated by narrow gaps or channelsfrom each other. FIG. 1 illustrates the present probe, indicated byreference number 10 in position for a measurement against a tire 12 withtreads 14. Gaps 16 are between treads 14. Probe 10 determines thedifference in radial distance between the bottom of gaps 16 and the topsof treads 14 and whether this difference meets whatever preselectedrequirements are imposed by the user or other authority.

Probe 10 comprises a generally cylindical housing 20 having a proximalend 22 and a distal end 24. Housing 20 is made of light-weight tubingsuch as aluminum, steel, plastic such as nylon, or composite materials.A handle 30 is fitted on proximal end 22 and an on/off button 36. Nearhandle is serial port 32 for connection to a small computer 40 withdisplay 42 and controls 44 via a cable 26. Computer 40 is preferably ofthe size of a palmtop computer such as that sold under the brand namePALM PILOT, CASSIOPEIA or PSION. These types of computers can receivedata into memory and process them for display and storage in a mannerwell known in the art. Stored data can later be downloaded to adifferent computer as desired.

Near proximal end 22 is a bracket 50 for engaging the side of tire 12for stability and to help in aligning probe 10, as will be describedmore fully below. Along the major axis of housing 20 is a window 60having, frame 62 with a slit 64 covered by an optical glass 66 to keepdust sad dirt out of housing 20. The length of slit 64 should be just aswide as the widest tire to be encountered.

Housing 20 is hollow, has a concave arcuate shape along one side at 28and is dimensioned internally to house a distance range finder 70 and acarrier assembly 80 for moving distance finder 70 along window 60 whileenabling range finder 70 to measure distance (Y-coordinate) from it totire 12 as it moves along housing 20 (X-coordinate) when probe 10 isproperly positioned against tire 12. Range finder 70 sends measurementdata to computer 40 by internal cable 72 for computation and display ofresults either through serial port 32 or IR (infrared) or RF (radiofrequency) transmission window 34 in the base of handle 30. By measuringdistance between the reference line, which is defined by the location ofthe distance finder 70 as it traverses housing 20, and the nearest pointon tire 12, the tire profile along its rolling face from side to sidecan be determined and, by subtraction from the reference, the differencein distance between the top of treads 14 and the bottom of gaps 16. Thisdifference will either meet or not meet a preselected criterion storablein computer 40. Computer 40 may be programmed to apply local criteria tothe distance measurement and thus produce an “OK” or “NOT OK” along withthe distance 92 and the profile 94, as shown in FIG. 3.

During operation, probe 10 is held against tire 12 with the plane ofwindow 60 parallel to the tangent of tire 12 and the two edges 52, 54 ofhousing 20 against the surface of tire 12 and bracket 50 against theside of tire 12. This “three-point” contact allows probe 10 to have acomplete view of tread 14's cross section and be stable for themeasurement. Stability is important to preserve the integrity of theline of reference to the tire defied by the movement of the range finder70

Range finder 70, which is mounted on the inside of housing 20 canmeasure the distance from a reference point to any opaque objectdirectly in front of it. Range finder 70 must have a range of operationnot less than one inch in front of it and not more than two inches awayfrom the device; that is, it must be capable of the measuring thedistance to an object as close as one inch and as distant as two inchesaway. This range allows range finder 70 to function through thethickness of the glass 64 and still have sufficient range to reach thebottom of a gap between treads of a deep truck tire. Range finder 70must have very tight field of view so as to be able to accurately detectthe edge of treads 14 and not produce false readings taken partially ontop of treads 14 and partially in gaps 16.

Range finder 70 employs a diode laser light source 74 and two linearposition sensors 76 arranged so as to be able to measure the distance totire 12 when probe 10 is positioned properly against tire 12. Lightsource 74 is fitted with optics to produce a tightly focused light spoton tire 12. Light is project toward tire 12 on a line which is parallelto a tire radius vector. An image of the spot on tire 12 is then focusedon the linear position sensor 76. Linear position sensors 76 produceelectrical signals proportional to the location of the spot on thesensor surface. The sensor is positioned at an angle to the laser sothat the location of the focused spot on the sensor therefore functionsas a laser triangulation distance measurement device.

The depth of gap 16 can be large compared to its width The narrow shapeof gap 16 can block the view of a single linear position sensor when thelaser spot is at the bottom of gap 16. This problem is most evident whenthe spot drops into gap 16 with the edge of tread 14 on the same side asthat position sensors. To improve measurements on in gaps 16, thepresent range finder 70 uses two position sensors 76. Sensors 76 aremounted at complementary angles on either side of laser light source 74.This improves the percentage of the width of the bottom of gaps 16 thatcan be measured.

To measure a compete cross section of tire 12, range finder 70 scansacross tire 12's width carried by carrier assembly. Range finder 70 ismounted on a linear be 82 and guided with a rod 84 mounted parallel tothe central axis of housing 20. A pulley 86, 88, is mounted at each endof rod 84 and motor-driven, toothed belt 90 is fitted between pulleys86, 88. The motor-driven belt 90 is used to move range finder 70 alongthe length of rod 84 while measurement is being taken. The motor is notshown since this type of mechanism, similar to that of a printer headcarrier is well known to those skilled in the art. See for example U.S.Pat. No. 5,162,916. Batteries 98 to power the range finder motor arelocated in handle 30.

The position of range finder 70 along rod 84 may be measured by adisplacement transducer (not shown) or tacked using a stepper motor (notshown) on belt 90.

The tread profile is a data set consisting of points containing anX-coordinate which is the position of range finder 70 on guide rod 84and a Y-coordinate which is the distance from range finder 70 to thesurface of tire 12. These coordinates are transmitted to computer 40 bymeans of suitable and conventional data link such as cable 72.

Computer 40 can produce a plot of the data points to enable the user toensure that the unit is functioning correctly. Display 42 shows a firstplot 92 of actual distance to tire 12, a second plot 94 showing thedifference in distance between a reference point on tread 14, and anindication as to whether the tread depth is sufficient or not accordingto a preselected criterion. Clearly various output can also be displayedfrom the received data, such as average and mean tread depth, minimumtread depth, and so on. Specific criteria as defined by local highwayregulators may be applied to determine if the tread is passable. Themeasurements may also be used to predict when tire replacement will berequired or the number of miles until tire replacement based oncomparison with stored data about a particular tire or tires in general.

In use, probe 10 is placed against the rolling face of a tire 12 andpushed against tire 12 so that bracket 50 engages the side of tire 12and window 60 is parallel to the tangent of tire 12 where the edges 52,54, of probe 10 meet tire 12. Range finder 70 and carrier assembly areactivated by pressing on/off button 36. Light source 74 on range finder70 transmits a beam of well focused light onto tire 12 through window 60and position sensors 76 adjacent light source 74 on range finder 70perceive the distance from range finder 70 to tire 12. The datareflective of that distance are transmitted through cable 72 to computer40 where the data is analyzed and displayed on display 42 for theoperator.

It will be apparent to those skilled in the art of tread depthmeasurement that many modifications and substitutions can be made to theforegoing description of preferred embodiments without departing fromthe spirit and scope of the present invention, defined by the appendedclaim.

What is claimed is:
 1. A probe for measuring tread depth, said probecomprising: a housing having a window formed therein, said housinghaving a proximal end and a distal end; range finding means for findingdistance, said range finding means being carried within said housing andoriented so that said range finding means directs a beam of lightthrough said window; means for moving said range finding means parallelto said window; means carried by said housing for gripping said housing;tire-engaging means carried by said housing for engaging a side and twolocations on a rolling face of a tire to provide a three-point contactfor preserving the integrity of a line of reference to the tire definedby the movement of said range finding means; and means carried by saidhousing and in operational connection with said range finding means andsaid moving means for sending distance data from said range findingmeans as said range finding means is moved parallel to said window whilea plane of said window is parallel to a tangent of the tire rolling facewhere engaged by said tire-engaging means.
 2. The probe as recited inclaim 1, wherein said housing has a concave arcuate shape with opposingedges for engaging the rolling face at two locations to support thehousing on a tire.
 3. The probe as recited in claim 1, furthercomprising a communications port means carried by said gripping meansfor communicating distance data to a computer.
 4. The probe as recitedin claim 3, wherein said communications port means transmits distancedata using an infrared transmission.
 5. The probe as recited in claim 3,wherein said communications port means transmits measurement data usinga radio frequency transmission.
 6. The probe as recited in claim 1,wherein said gripping means is a handle carried by said proximal end ofsaid housing.
 7. The probe as recited in claim 3, further comprising ahandheld computer, said handheld computer being in electricalcommunication with said range finding means, and said handheld computerhaving a display and means for plotting distance data.
 8. A probe formeasuring tread depth, said probe comprising: a housing having a windowformed therein, said housing having a proximal end and a distal end;range finding means for finding distance, said range finding means beingcarried within said housing and oriented so that said range findingmeans directs a beam of light through said window; means carried by saidhousing for gripping said housing; tire-engaging means carried by saidhousing for engaging a side and two locations on a rolling face of atire to provide a three-point contact for preserving the integrity of aline of reference to the tire defined by the movement of said rangefinding means; means for moving said range finding means parallel to theline of reference; and means carried by said housing and in operationalconnection with said range finding means and said moving means forsending distance data from said range finding means as said rangefinding means is moved parallel to the line of reference while a planeof said window is parallel to a tangent of the rolling face whereengaged by said tire-engaging means.
 9. The probe as recited in claim 8,wherein said range finding means measures distance to said tire face bytriangulation.
 10. The probe as recited in claim 8, wherein said rangefinding means further comprises two sensors and a light source fordirecting said beam of light, said sensors located on either side ofsaid light source.